Boat propeller



Feb. 2, 1954 w. P. CLARK 2,667,936

BOAT PROPELLER Filed Sept. 16; 1950 2 Sheets-Sheet 1 T am-,2

I N V EN TOR. WIT/[am F. C far/E Feb. 2, 1954 w, F. L RK 2,667,936

BOAT PROPELLER Filed Sept. 16, 1950 2 Sheets-Sheet 2 IN VEN TOR. Wf/l/am5' Clark Patented Feb. 2, 1954 "UNITED STATES PATENT OFFICE BOATPROPELLER William F. Clark, Portland, 'Oreg.

Application September 16, 1950, Serial No. 185,281

1 Claim.

'The present invention comprises an improvement in propellers for boats,the invention being such that increased efficiency and increased speedsare achieved. An object of the-invention is to provide a propeller withmeans for reducing turbulence and thus increasing the effective thrustof the blades, and eliminating drag and corrosion due to cavitation. Theprinciples of the invention may be applied to a propeller havingnormally positioned or raked blades in accordance with the choice of thedesigner.

The objects and advantages of the present invention may be more readilyascertained by inspection of the following specification taken inconnection with the accompanying drawing wherein like numerals refer tolike parts throughout, while the features of novelty will be moredistinctly pointed out in the appended claim.

In the drawing, Fig. 1 is a plan view of a portion of a normal propellerlooking toward the 6 working surface of one of the blades;

Fig.2 is a rear view looking toward the back surface of one of theblades;

Fig. 3 is a side elevation showing the back surface of one of theblades;

Fig. 4 is a vertical section taken substantially along line l l of Fig.3;

Fig. 5 is a vertical section taken substantially along line 55 of Fig.3;

Fig. 6 is a development layout for the blade; and.

Fig. '7 is an end view of a blade having the sections developed in Fig.6 applied thereto.

A propeller constructed in accordance with my invention comprises acylindrical hub 10 from which a plurality of blades H extend. Each ofthe blades comprises a leading edge l2 commencing at a point near onelongitudinal end of the hub and a trailing edge 13 commencing at a pointnear the other longitudinal end of the hub, the two edges merging at theouter end of the blade along a curved line in accordance with usualpractice. The exact outline of the blade is immaterial, the presentillustration being of a blade having a substantially elliptical shape,the outer portion being substantially circular about a point taken alonga central radius, the radius of the circle being such as to define thedesired working surface area.

As seen in Fig. 6, any arcuate section of the blade taken along theintersection of a cylinder having its axis coincident with the axis ofthe hub comprises a curved line along the back surface of the blade, thecurvature of the line being such as to comply with design requirementsfor the thickness of the blade along its central radius. These sectionsare indicated in dotted lines at 16, the Working surface portionsthereof extending along lines from the point I! which is a pointalongthe longitudinal axis of the hub at a distance from the center of thehub equal to the pitch divided by 2 pi, the lines extending from thepoint I! to points along the central radius of the working surfaceextending from the longitudinal center of the hub at I8 to the tip ofthe blade indicated at I9. The line |8-l9 may be considered to be aportion of a plane including the outer portion of a radial line definingthe center of the blade and the longitudinalaxis of the hub. The radialelement of the working surface of the blade indicated in Fig. 6 extends"radially from the point 20 which is arbitrarily selected as beingsomewhere between .3 and .5 of the radius of the blade. Inwardly fromthe point 20 the-working surface of the blade taken along a plane normalto the axis of the hub is defined by a curve tangent to the outersurface of-the hub, the point of tangency 2| being rearward with respectto the direction'of rotation from the plane including the axis of thehub. The rear surface of the blade may be laid out by determining thecentral thicknesses of the respective transverse sections I6 and thusdrawing a corresponding line l9-22--2324. This line l9-22--23-24represents the rear edge of a section normal to the working surface ofthe blade including the line l9-20-2l. From l9 to 22 it is a straightline, from 22 to 23 it is a curved line somewhat parallel to the portion20-2l, and from 23 to 24 it is an arbitrarily selected curved lineforming a reverse curve with the portion 22-23 and terminating tangentto the hub of the propeller. The portion of the line from 23 to 24 is ofarbitrarily selected curvature designed to fair the rear surface of theblade into the hub. Similar sections perpendicular to the workingsurface may be laid out for any other portion of the blade by drawinglines parallel to the line l8-l9 and measuring the thicknesses of thesection l6 at the point where the lines intersect.

In Fig. 1 the line l8-I9 is laid out as shown and comprises the centralradius of the blade. The point 20 is indicated at the section of thearcuate line It at substantially .4 of the radius of the blade and thesweep back at the intersection of the horizontal plane with the workingsurface of the blade is indicated by the line 2l]-2l to the point oftangency with the outer surface of the hub. It is to be appreciated thatthe acute angle between the hub and the blade is partially filled in bya strengthening fillet 28 which is made as small as practicable. Aplurality of other radii are drawn from the axis of the hub I8 and aplurality of other elements taken along planes normal to the axis of thehub are also indicated in dotted outline, each of the elements beingstraight radial lines beyond the arcuate line H at .4 of the radius ofthe blade and being swept back with respect to the direction of rotationto a point of tangency with the outer surface of the hub.

Figs. 4 and 5 are sections taken through the blade along planes normalto the axis of the hub. In Fig. 4 it will be seen that the intersectionof the plane with the working face of the blade is a straight line froma point 25 at the edge of the blade to a point 26 along the are passingthrough point 20 and is a curved line tangent to the outer surface ofthe hub from the point 26 to the point 21. The line of intersection ofthe plane with the rear surface of the blade is of irregular contourdetermined by the development previously explained. The fillet 28 isindicated in this figure. Fig. 5 is a similar section with the elementdefined by the horizontal plane being a straight line from point 30 tothe point 3i taken along the arcuate line passing through point 20 andis then a curve swept back to the point of tangency at 32, the fillet 28being indicated in this view as well. In Figs. 4 and 5 it is apparentthat the working surface is swept back from a vertical plane includingthe line 25-.26 and the axis of the hub.

It should be apparent from the foregoing that turbulence would bedecreased to an absolute minimum since the working surface from a pointbetween a third and a half of the radius of the blades is rakedrearwardly with respect to the direction of rotation. Inwardly from thecenter of the blade the rearward rake thereof forces the water towardthe hub to a certain extent, thus counteracting the outward thrust ofthe blade and causing the water to be directed toward the axis of theblade without turbulence, and eliminating eddying and pocketing behindthe blade.

Having illustrated and described a preferred embodiment of my invention,it should be apparent to those skilled in the art that the inventionpermits of modification in arrangement and detail. I claim as myinvention all such modifications as come within the true spirit andscope of the appended claim.

I claim:

A propeller comprising a cylindrical hub and a plurality of bladesextending from the hub, each of said blades having its leading edgestarting from a point near one longitudinal end of the hub and itstrailing edge starting from a point near the other longitudinal edge ofthe hub, the working surface of each of said blades being such that anyelement thereof defined by the intersection of a plane normal to theaxis of the hub is a straight radial line beyond the center of the bladeand a curved line tangent to the outer surface of the hub inwardly fromthe center of the blade, the point of tangency being rearward withrespect to the direction of rotation from a plane including the axis ofthe hub and the straight radial portion of the element.

' WILLIAM F. CLARK.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 368,416 Mosher Aug. 16, 1887 413,268 Tonns Oct. 22, 1889619,136 Carver Feb. 7, 1899 832,173 Taylor Oct. 2, 1906 1,371,610 DunganMar. 15, 1921 1,733,251 Deering Oct. 29, 1929 FOREIGN PATENTS NumberCountry Date 15,254 Great Britain of 1902 26,280 Netherlands Mar. 15,1932 290,677 Italy Nov. 25, 1931

